1. Field of the Invention
This invention relates to the coaxial cable communications art.
More particularly, the present invention relates to signal coupling outlets of the type to which terminating mechanisms or user devices are removably coupled into a system, employing coaxial cables to effect communications between the system constituents.
In a further and more specific aspect, the instant invention concerns an improved outlet especially adapted for deep signal attenuation upon disconnection of a normally connected user terminating device.
2. Background Information
It is common practice in coaxial cable communications systems for a plurality of terminating mechanisms to be coupled with a central signal processing unit. Exemplary is the familiar community antenna television (CATV) in which a single antenna is employed to receive an airborne signal and associated circuitry is employed to subsequently retransmit the signal, via coaxial cable, to the several monitors in the system. Also representative is the local area network (LAN) typified by a centralized data processing unit which communicates with one or more remotely located computer terminals.
Commonly, signals are coupled between the central unit and each remote device (and in certain installations, among the several remote devices) by means of coaxial cables. A drop line, typically a coaxial cable extending from the main or trunk line, terminates with an outlet in the vicinity of the respective remote device. The device is coupled into the system by means of an integral coaxial cable fitted with a connector which is detachably coupleable with the outlet.
The remote devices used in such systems may be generally characterized as being somewhat portable. Thus, for various reasons including maintenance, relocation or discontinuation of need, a particular device may be periodically or permanently withdrawn from service and removed from the system. Coincidentally, the connector is disengaged from the outlet.
Those skilled in the art will appreciate that low level system signals in the form of electromagnetic waves will radiate from an open, unterminated outlet thereby contributing to environmental electromagnetic interference. Recently, there has been an increased awareness and concern over the crowding of the electromagnetic spectrum threatening the environment with "electromagnetic pollution" as a result of the proliferation of electronic devices which function as electromagnetic interference sources. The desirability of securing an unused signal outlet to eliminate such radiation is therefore immediately apparent.
In addition, to maintain system integrity, it is imperative that each unused outlet be secured. In a CATV system, for example, the signal loss through an open outlet contributes to a general pollution of the communications spectrum and degraded performance of other devices, such as radios and television receivers, in the vicinity. Conversely, electromagnetic interference entering through an open outlet will cause distortion and effect other system degradations on other terminal devices still in use within the system.
The problem is of substantially greater significance in a local area network system, both as to radiation emission and reception. Frequently, an LAN system is intended to be available only to authorized personnel, and the signals occurring within the system may contain data and information which is proprietary or even of sufficient sensitivity as to affect the commercial or even national security. Similarly, the signals may require critical accuracy in the communications process. Unintentional or unauthorized reception of electromagnetic interference through an open outlet is capable of interrupting system operation and/or of altering or destroying the fidelity of transmissions and data. The open outlet also represents a potential serious breach of security since the radiating signal can be received by a remotely located unauthorized receptor. Further, the system itself may be deliberately accessed wirelessly through an open outlet to alter or destroy system information.
In attempting to remedy the foregoing problems, and to insure electromagnetic compatability, various purported solutions have been proposed in the prior art. A relatively uncomplicated and effective solution is in the form of a metal cap which is engaged with the outlet in lieu of the the removed cable connector. While effectively terminating the outlet, the cap device has been proven to be less than a satisfactory solution to the problem. As a result of inherent human foibles, especially when the primary concern is relocation of the terminal device, the act of placing the cap over the end of the outlet is frequently forgotten. Further, the cap (being relatively small) is easily lost. Also, if the cap is not properly attached, increased, rather than decreased, radiation can result. Finally, where unauthorized access to the system is sought, the cap may simply be surreptitiously removed.
To alleviate the problems associated with the above described cap, the prior art has provided self terminating outlets. Such devices generally include internal mechanisms which open upon the engagement of a connector and close upon disengagement. While being convenient to use, self-terminating outlets have not proven entirely effective in preventing radiation or reception of signals, either intentionally or unintentionally. Further, being relatively cumbersome and expensive to manufacture, the internal mechanism of such devices are subject to failure as a result of mechanical breakage or environmental deterioration such as the deposit of oxide layers which can defeat the self-terminating effect.
Thus, those skilled in the art will appreciate that it would be highly advantageous to remedy the foregoing and other deficiencies inherent in the prior art and to provide a very effective, yet simple, solution to the problem of terminating coaxial conductors to prevent communication to and from the open outlet when a user device has been removed.